A considerable number of tannic acids occur in nature. Chemically, these acids are described as polymers of different hydroxybenzoic acids. Generally, when the term tannic acid is employed, as in the present case, the acid referred to is gallotannic acid, the internal ester of gallic acid also frequently referred to as tannin.
Tannic Acid consists of an amorphous powder glistening scales or spongy masses varying in color from yellowish-white to light brown. Tannic acid is very soluble in water, glycerine or alcohol.
Tannic acids are usually obtained from glycosides which consist of several molecules of a tannic acid in combination with glucose.
Commercially available, tannic acid, also known as Tannin, has a complex non-uniform chemistry usually contains from about 5% to about 10% by weight water, has a molecular weight of about 1700 and is typically produced from Turkish or Chinese nutgall.
Carbetapentane, 2-(2-diethylaminoethoxy)ethyl-1 phenylcyclopentane carboxlate is an antitussive compound that is described in U.S. Pat. No. 2,842,585 and is structurally related to caramiphen. Carbetapentane citrate has a melting point of 93.degree. C. and occurs as a white powder freely soluble in water and slightly soluble in alcohol.
Carbetapentane has an atropine-like action that depresses the cough reflex by selective central nervous system depression.
Pyrilamine is one of the oldest and most enduring antihistaminic drugs, known chemically as N-[(4-methoxyphenyl)methyl]-N',N'-dimethyl-N-2-pyridinyl-1,2-ethanediamine , its preparation is disclosed in U.S. Pat. No. 2,502,151 and is an oily liquid. Pyrilamine hydrochloride salt is very soluble in water and has a melting point of 143-143.50.degree. C. whereas the maleate salt is slightly soluble in water, benzene and ether and has a melting point of 100-101.degree. C.
Antihistamine compounds in the form of their free bases as well as their salts, e.g. hydrochloride, citrate, maleate, tannate, etc., are well known. Antihistamines in the form of their tannate salts are very desirable because such salts are generally stable and may be combined in such form without any untoward side effects.
Antihistaminics and antitussives in the form of their tannate salts are typically prepared by reacting the free base, e.g. pyrilamine, carbetapentane, etc. with tannic acid in the presence of a volatile solvent, usually isopropanol. Typically, in the conventional isopropanol route, the decongestant or antihistaminic free base and the tannic acid will be present in the isopropanol at a concentration of about 20% based on the weight of the reaction mixture. The reaction mixture is stirred for about one hour while maintaining the mixture at 60-70.degree. C. The reaction mixture is cooled to room temperature and then filtered, washed with isopropanol and then vacuum dried. Alternative routes to the tannate salts are described in U.S. Pat. Nos. 5,599,846 and 5,663,415.